Sequential expression of three known protective genes in cardiac biopsies after transplantation

The expression of the "protective" genes A20, heme oxygenase (HO)-1, and Bcl-xl in rodent allografts and xenografts correlates with long-term survival of transplanted hearts. We investigated the expression of HO-1, Bcl-2, and A20 in sequential biopsies from nine cardiac transplant recipients by using quantitative real-time reverse-transcriptase polymerase chain reaction and immunohistochemistry.

Five to 16 endomyocardial biopsies were analyzed from each patient 7 to 365 days after transplantation. Biopsies were classified as acute rejection (AR) by International Society of Heart and Lung Transplantation criteria. mRNA values were normalized against an endogenous control gene (18S), and protein expression was analyzed by immunohistochemistry.

All genes were expressed at every time point. HO-1 was significantly higher in the first 2 months (2 months vs. 10+ months, P<0.05) and was associated with AR (0.30+/-0.07) versus nonrejection (0.16+/-0.02, P=0.026). In contrast, expression of Bcl-2 and A20 was low at 2 months, but both increased with time (P<0.05, 2 months vs. 10+ months for Bcl-2 and A20). There was no significant association of Bcl-2 or A20 with AR. Immunocytochemistry revealed that HO-1 localizes to infiltrating cells and not parenchymal cells in cardiac biopsies. In contrast, Bcl-2 and A20 were found to localize to endothelial, smooth muscle, and infiltrating cells.

HO-1 is induced early after transplantation, whereas Bcl-2 and A20 seem to be induced as part of the chronic response. These differences together with different localization sites in vivo suggest they have different roles in protection from injury after cardiac transplantation.